From my 2017 post-trip write up...
Water
Earlier trip reports stress the importance of adequate hydration, with the 2006 report suggesting that 3 litres was only enough to get you to the bottom and that puritabs, boiling, or a water pump would be required to provide further drinking water. The report also suggested drinking large amounts of water prior to entering the cave to hyperhydrate and thus delay dehydration. We tried this to some extent, but forcing ourselves to drink water made us feel a bit sick.
On the deep trip we each carried in 3l of water. We stashed another 1.5l bottle of water at the foot of Garby?s for dehydrated cavers to use on the way out. Another extra 1.5l bottle was left at Camp 1. We carried puritabs to purify any water that we refilled from the stream.
Surprisingly, we drank less than a litre on the way to the bottom, and didn?t finish off the remaining two litres on the way back up. The water left at Camp 1 and Garby?s was not required and was simply poured onto the floor to save weight. We were probably a little bit dehydrated on exiting the cave, but this was no big deal.